Once a rarity, this was the fifth female suicide attack this year and the eighth since November.

Also Sunday, two American soldiers were killed, and a U.S. military spokesman said soldiers continue to find weapons caches connected to Iranian-backed militia groups.

In the market in the Karrada neighborhood of east Baghdad, the woman ran from a checkpoint when Iraqi security spotted wires coming from the sleeve of her black beggar's clothes.

She ran toward some shops. Sameer Ahmed saw the woman's face and the wires wrapped around her body. In her mid-30s, she held one of the wires in her hand.

"I am going to explode myself if you come near me!" Ahmed, 43, recalled her warning.

Another shopkeeper brought an assault rifle out of his shop and fired at the woman and she exploded, either by the bullets triggering the bomb or by her own actions, Ahmed said. A military report said it was an Iraqi soldier who fired at the woman, saying she staggered back before detonating near a car. The report also said no one was killed and suggested her possible target was an Iraqi colonel touring the area.

Ahmed said the woman did not appear mentally impaired, which is how police officials described two women bombers in two market bombings on Feb. 1 that killed 99.

Sunday's blast occurred near Sadoon Street, one of the most famous streets in Baghdad. Shop windows blew out and Yassen Zaid, 32, took cover behind a refrigerator in a shop.

He was shopping for a new washing machine for his wife.

"It was terrible," said Zaid, still in shock from the incident an hour later. "I saw police and people helping two injured people. I left the scene at once and forgot the washing machine I came for."

North of Baghdad in Diyala province, two U.S. soldiers were killed by small arms fire. Another soldier was wounded, according to a military press release. No further information was available pending notification of relatives.

Also Sunday, U.S. spokesman Rear Adm. Greg Smith announced the discovery of two large weapons caches that are tied to Iranian-backed "special groups," a term used by the military to describe Iraqis who go to Iran to receive training and return to train others and plan attacks against U.S. forces.

Combined, the two caches had more than 300 mortar rounds, more than 900 anti-aircraft rounds, 50 rocket sleds and 100 pounds of explosives.

"Finding these large caches is not reassuring," Smith said. It wasn't clear if the groups with the caches were waiting for specific orders or had plans in the works, he said.

While a six-month ceasefire has stopped much of the attacks by the Mahdi Army militia, there has been no decrease in special groups activity, Smith said.

Smith couldn't say if there was any direct connection with the Iranian government, but he said U.S. officials continue to think it contributes support.

"The intent of Iran in supporting the training and financing of these groups we believe continues, but what we don't know precisely is whether or not there is any direction coming from Iran in how they conduct their operations inside of Iraq," he said. "We do think the training and financing of those activities remains in place."